The invention relates to a device for the variable adjustment of the control times for gas-exchange valves of an internal combustion engine according to the preambles of claims 1 or 5.
In internal combustion engines, camshafts are used for actuating the gas-exchange valves. Camshafts are mounted in the internal combustion engine such that cams mounted on the camshafts contact cam followers, for example, cup tappets, finger levers, or rocker arms. If a camshaft is set in rotation, then the cams roll against the cam followers, which, in turn, actuate the gas-exchange valves. Through the position and the shape of the cams, both the opening period and also the opening amplitude, but also the opening and closing times of the gas-exchange valves are set.
Modern engine concepts are moving towards a design with a variable valve drive. On one hand, the valve stroke and valve opening period should be able to be shaped variably up to the complete shutdown of an individual cylinder. For this purpose, concepts, such as switchable cam followers or electro-hydraulic or electrical valve actuators are provided. Furthermore, it has been shown to be advantageous to influence the opening and closing times of the gas-exchange valves during the operation of the internal combustion engine. Here, it is especially desirable to influence the opening or closing times of the intake or exhaust valves separately, in order to selectively set, for example, a defined valve overlap. By adjusting the opening or closing times of the gas-exchange valves as a function of the current engine-map range, for example, the current rotational speed or the current load, the specific fuel consumption can be reduced, the exhaust-gas behavior can be positively influenced, and the engine efficiency, the maximum torque, and the maximum output can be increased.
The described variability of the valve control times is achieved through a relative change in the phase position of the camshaft relative to the crankshaft. Here, the camshaft is usually in driven connection with the crankshaft via a chain, belt, or gear drive or a driving concept with an identical function. Between the chain, belt, or gear drive driven by the crankshaft and the camshaft there is a device for changing the control times of an internal combustion engine, also called camshaft adjuster below, which transfers the torque from the crankshaft to the camshaft. Here, this device is constructed so that during the operation of the internal combustion engine, the phase position between the crankshaft and the camshaft can be held securely and, if desired, the camshaft can be rotated within a certain angular range relative to the crankshaft.
Belt-driven camshaft adjusters are usually arranged outside of the cylinder head. Here, care must be taken that the camshaft adjuster must be completely sealed from the surroundings, in order to prevent the leakage of motor oil into the engine compartment. Any leakage oil must be captured and led back into the cylinder head.
In internal combustion engines with separate camshafts for the intake valves and the exhaust valves, these can each be equipped with a camshaft adjuster. Therefore, the opening and closing times of the intake and exhaust valves can be shifted in time relative to each other and the valve overlap can be adjusted selectively.
The position of modern camshaft adjusters is usually located on the driving-side end of the camshaft. The camshaft adjuster, however, can also be arranged on an intermediate shaft, a non-rotating component, or the crankshaft. It is made from a drive wheel, which is driven by the crankshaft and which keeps a fixed phase relationship relative to this crankshaft, a driven part in driving connection with the camshaft, and an adjustment mechanism transferring the torque from the drive wheel to the driven part. The drive wheel can be constructed, in the case of a camshaft adjuster not arranged on the crankshaft, as a chain, belt, or gear and is driven by the crankshaft by a chain, belt, or gear drive. The adjustment mechanism can be operated electrically (by a driving triple-shaft gear mechanism), hydraulically, or pneumatically.
A preferred embodiment of the hydraulic camshaft adjuster is the so-called rotary piston adjuster. In this embodiment, the drive wheel is locked in rotation with a stator. The stator and a driven element are arranged concentric to each other, wherein the driven element is connected non-positive, positive, or form fit, for example, by a press fit, a screw connection, or a weld connection, to the camshaft, an extension of the camshaft, or an intermediate shaft. In the stator, several hollow spaces spaced apart in the circumferential direction are formed, which extend radially outward from the driven element. The hollow spaces are defined in a pressure-tight way by side covers in the axial direction. Into each of these hollow spaces extends a blade, which is connected to the driven element and which divides each hollow space into two pressure chambers. Through selective connection of the individual pressure chambers to a pressurized medium pump or to a tank, the phase of the camshaft can be adjusted or held relative to the crankshaft.
For controlling the camshaft adjuster, sensors detect the characteristic data of the engine, such as, for example, the load state and the rotational speed. This data is fed to an electronic control unit, which controls the inflow and outflow of pressurized medium to and from the different pressure chambers after comparing the data with a characteristic data map of the internal combustion engine.
To adjust the phase position of the camshaft relative to the crankshaft, in hydraulic camshaft adjusters, one of the two pressure chambers of a hollow space acting against each other is connected to a pressurized medium pump and the other is connected to the tank. In this way, the pressurization of one chamber and the release of pressure in the other chamber displace the blade and thus directly cause a rotation of the camshaft relative to the crankshaft. To keep the phase position, both pressure chambers are either connected to the pressurized medium pump or both are separated from the pressurized medium pump and also the tank.
The pressurized medium flows to or from the pressure chambers are controlled by a control valve, usually a 4/3 proportional valve. Each valve housing is provided with a connection for the pressure chambers (working connection), a connection to the pressurized medium pump, and at least one connection to a tank. Within the essentially hollow cylindrical valve housing there is a control piston that can be shifted in the axial direction. The control piston can be brought into each position between two defined end positions in the axial direction via an electromagnetic actuator against the spring force of a spring element. The control piston is further provided with annular grooves and control edges, whereby the individual pressure chambers can be connected selectively to the pressurized medium pump or to the tank. Likewise, a position of the control piston can be provided, in which the pressure chambers are separated both from the pressurized medium pump and also from the pressurized medium tank.
Such a device is disclosed in DE 199 08 934 A1. This involves a device with a rotary piston construction. A stator is supported so that it can rotate on a driven element locked in rotation with a camshaft. The stator is constructed with recesses open to the driven element. In the axial direction of the device, compensating disks are provided, which define the recesses in the axial direction in a sealing manner. The recesses are closed in a pressure-tight manner by the stator, the driven element, and the compensating disks and thus form pressure spaces. On the outer casing surface of the driven element there are blades, which extend into the recesses. The blades are constructed so that they divide the pressure chambers into two pressure chambers acting against each other. By supplying or discharging pressurized medium to or from the pressure chambers, the phase position of the driven element can be selectively maintained or adjusted relative to the stator and thus the camshaft relative to the crankshaft. For this purpose, a device for the pressurized medium supply is provided with pressurized medium lines and a control valve.
The stator, the driven element, and the compensating disks are encapsulated by a two-part housing, which is locked in rotation with a drive wheel constructed as a toothed belt wheel.
The flat bases of the housing halves ensure a pressure-tight contact of the compensating disks on the stator and the driven element.
In addition, the driving torque of the crankshaft is transferred to the stator with a friction fit via the drive wheel and the bases of the compensating disks. Alternatively, it is proposed that the side surfaces of the stator have profiling, whereby an additional positive fit can be achieved.
In this embodiment, a large number of components are required for realizing the device, whereby increased assembly costs and thus production costs occur. In addition, the described transmission of the torque from the drive wheel to the stator is associated with increased production expense, which has a negative effect on the costs of the device.